<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>promp.html</title>
</head>
<body>
    <script>
        var a,b,sum;
     a= Number(  prompt ('请输入第一个数'));
     b=Number(  prompt ('请输入第二个数'));
     sum=a+b;
     alert(a+'加上'+b+'等于'+sum);
    

    </script>
</body>
</html>